Issues and Improvements in TCP Performance over Multihop Wireless Networks

Modern network technologies first evolved in wired networks and subsequently entered the wireless network field. Applications may work in pure wired network, pure wireless network or hybrid network. Improving performance in these network infrastructures has been a continuous effort for decades. In this dissertation, we tackle two important challenges: (1) improving handover performance in heterogeneous wireless network, and (2) improving TCP performance in multi-hop wireless network. In heterogeneous network, users expect uninterrupted services moving from one network to another. IEEE proposed Media Independent Handover (MIH) to make it possible to achieve better handover performance. Currently, Mobile IPv4 (MIP) is the dominant mechanism for mobility management and is expected to persist into the future. However, when multiple interfaces of a mobile client are connected to a Foreign Agent (FA), MIP and its existing improvements do not perform well when the active interface fails unexpectedly. In this dissertation, we propose novel mechanism and MIP extension with MIH support. We prove experimentally that the new approach eliminates the FA-HA latency and achieves much faster handover, compared with existing mechanism. Our method also allows FA-bicasting, which can improve transmission reliability by combining traffic from different links, through the same FA. In multi-hop wireless networks, the main network factor that affects TCP performance is the medium-access contention, complicated by other factors like hidden terminal. We analyze the TCP congestion window and provide a more accurate estimate of its optimal value than those reported in the prior work. We also show that the much shorter TCP-ACK packets consume comparable channel capacity as the much longer data packets. We therefore propose two methods to improve TCP throughput, as follows. (1) Segregate the flows of data and ACK using static routing in grid wireless network, (2) Develop an improved variant of delayed TCP ACK by minimizing the number of ACK packets. Our evaluation validates the effectiveness of the proposed method, which can enhance TCP performance significantly. In terms of throughput, it achieves up to 204% improvement over the regular TCP in chain-topology wireless networks, and about 35% improvement in a complex grid wireless network. We also propose a new architecture to achieve higher throughput when multiple TCP connections exist.

In this study we investigate the interaction between TCP and MAC layer in a wireless multi-hop network. This type of network has traditionally found applications in the military (automated battlefield), law enforcement (search and rescue) and disaster recovery (flood, earthquake), where there is no fixed wired infrastructure. Wireless "ad-hoc" multi-hop networks have previously been proposed for nomadic computing applications. Key requirements in all the above applications are reliable data transfer and congestion control, features that are generally supported by TCP. Unfortunately, TCP performs on wireless in a much less predictable way than on wired protocols. Using simulation, we provide new insight into two critical problems of TCP over wireless multi-hop. The first is the conflict between data packets and ACKs, which causes TCP performance to degrade for window sizes greater than 1 packet. The second is the interaction between MAC and TCP layer backoff timers which causes severe unfairness and capture conditions. In the paper, we identify these problems in several representative simulation runs on various topologies and traffic patterns and indicate possible remedies to improve TCP efficiency over a wireless multi-hop network.

In a multihop wireless network, the throughput performance decreases seriously because of inter-flow and intra-flow collision. The backoff algorithm is the de facto function to resolve collision in 802.11 networks. In this paper we study the impact of five back-off algorithms on the performance of 802.11-based multihop wireless networks with different network topology and flow patterns. Simulations show that the backoff algorithms have big influence on the performance of both UDP and TCP flows. But none of the current backoff algorithms can improve the throughput and fairness performance in multihop wireless networks efficiently. It shows that the traditional random backoff algorithms are no longer suitable for collision resolution in distributed multihop wireless networks.

While TCP is highly successful in the wire-line Internet, its performance fast degrades as the number of hops increases in multihop wireless networks It is due to not only the half-duplex nature of the wireless medium, but also the two-way feature of TCP In order to improve TCP performance in multihop wireless networks, we pay attention to its cumulative ACK policy Systematically exploiting the redundant nature of the ACK policy, we replace some ACKs with data packets We call this scheme block acknowledgement In consequence, the throughput is significantly increased at the slight weakening of ACK reliability We evaluate the performance of TCP with and without the block acknowledgement through simulations and analysis.

Secure performance enhancing proxy: To ensure end-to-end security and enhance TCP performance over IPv6 wireless networks

In a multi-hop wireless network, connectivity is determined by the link that is established by the receiving signal strength computed by subtracting the path loss from the transmission power. Two path loss models are commonly used in research, namely two-ray ground and shadow fading, which determine the receiving signal strength and affect the link quality. Link quality is one of the key factors that affect network performance. In general, network performance improves with better link quality in a wireless network. In this study, we measure the network connectivity and performance in a shadow fading path loss model, and our observation shows that both are severely degraded in this path loss model. To improve network performance, we propose power control schemes utilizing link quality to identify the set of nodes required to adjust the transmission power in order to improve the network throughput in both homogeneous and heterogeneous multi-hop wireless networks. Numerical studies to evaluate the proposed schemes are presented and compared.

This paper addresses the Quality of Service (QoS) degradation problem of wireless relay node failures in multihop Worldwide interoperable Microwave Access (WiMAX) and Long Term Evolution (LTE) networks. In general, node protection in a communication network increases the reliability of the traffic flow from source to destination. For wireless networks, implementing the traditional 1+1 protection scheme increases the capital cost, as resources cannot be fully utilized. On the other hand, the design and implementation of the 1:N protection scheme in wireless networks for greater value of N (> 2) is very difficult, due to wireless network coverage and the physical layer design. To overcome the above drawbacks, a technique based on network coding is proposed for node protection in multihop wireless networks. In multihop wireless networks, few research efforts are concentrated on node protection schemes using network coding. Moreover, to best of our knowledge, no reports have been published on measuring the QoS performance for node protection in 4G wireless networks using network coding. In this paper, we first describe the node protection scheme using XOR network coding for multihop 4G wireless networks. Then, we measure the QoS performance, such as packet delivery ratio (PDR), latency and jitter, for different scenarios. The scenarios include a failure of a single relay node and failures of two relay nodes with and without our protection scheme and user's mobility. The simulation results show that the QoS performance with protection against a single relay node failure and failures of two relay nodes are very close to that of no failure scenario, while the network reliability increases due to the protection mechanism. Also, we report a decoding problem in multihop wireless networks using XOR network coding.

Mobile computing and security in Internet have become two of the most important challenges in the information technology world. Among wireless technologies which support user mobility, satellites will play a very important role. Unfortunately, TCP does not perform well on satellite channels because of the related high delay-bandwidth product, high bit error rate (BER) and burst errors mainly due to shadowing. In order to obtain improvements in TCP performance, an approach local to the satellite link could be adopted. In fact, recently, some studies showed the effectiveness of the use of a reliable data link protocol that is well suited to mobile geo-stationary satellite channel characteristics. However, the resultant more variable end-to-end delay causes, as a side effect, a new problem: the competition between retransmission mechanisms at transport layer and data link layer. The introduction of a suitable performance enhancing proxy (PEP) on the satellite gateway has proved to be a viable technique to face the problem. However, the compatibility with the usage of network layer security mechanisms, such as IPSec, should be pursued. This paper just deals with the definition of an IPSec-aware TCP PEP, called secure PEP (SPEP), that is completely transparent to IPSec architecture. The performances of SPEP have been validated in the context of Web application by using network simulator tool. The simulation results, in terms of Web-page download mean time, have shown that the proposed solution provides substantial improvements in TCP performance.

Wireless LANs have been widely deployed as edge access networks in home/office/commercial buildings, providing connection to the Internet. Therefore, performance of end-to-end connections to/from such WLANs is of great importance to network applications and end-users. The advent of Dynamic Spectrum Access (DSA) technology is expected to play a major role in improving wireless communication. With DSA enabled, WLANs opportunistically access licensed channels in order to enhance spectrum-usage efficiency, and provide better network performance. In this paper, we explore issues and solutions in realizing this potential of DSA. We first identify the key issues that impact end-to-end TCP performance when a DSA-enabled WLAN is integrated with the wired cloud. Then, we propose a new network management framework, called DSASync, to eliminate or mitigate the performance issues we identified. DSASync requires no modifications to the fixed wired network or existing network stack, while ensuring traditional TCP semantics to be obeyed. DSASync uses a combination of buffering and traffic-shaping algorithms to minimize the adverse side-effects of DSA on the TCP flows. Finally, we evaluate DSASync through a prototype implementation and deployment in a testbed. The results show significant improvements in TCP performance, e.g., a 74 increase in downlink goodput, making it a promising step forward towards applying DSA technology in consumer WLANs.

Improving TCP performance over wired–wireless networks

The performance of a multihop wireless network is typically affected by the interference caused by transmissions in the same network. In a statistical fading environment, the interference effects become harder to predict. Information sources in a multihop wireless network can improve throughput and delay performance of data streams by implementing interference-aware packet injection mechanisms. Forcing packets to wait at the head of queues and coordinating packet injections among different sources enable effective control of copacket interference. In this paper, throughput and delay performance in interference-limited multihop networks is analyzed. Using nonlinear probabilistic hopping models, waiting times which jointly optimize throughput and delay performances are derived. Optimal coordinated injection strategies are also investigated as functions of the number of information sources and their separations. The resulting analysis demonstrates the interaction of performance constraints and achievable capacity in a wireless multihop network.

An ad hoc network is a dynamically forming temporary network with a collection of wireless mobile nodes. It does not use any centralized administration or existing network infrastructure. In wireless networks, improving TCP performance largely depends on congestion window size. Both contention and congestion affect the TCP performance. A contention problem occurs in network when adjacent nodes shared channel to transmit packets. Channel contentions cause network congestion because of a lack of coordination between the transport layer and the medium access layer. Due to the channel interference the Bandwidth Delay Product cannot reach to maximum value as in wired network. Packet loss occurs at MAC layer due to congestion. In ad hoc networks, both contention and congestion can severely affect the performance of TCP. In our work, we show that the over-injection of conventional TCP window mechanism results in severe contentions, and medium contentions cause network congestion. The idea is to dynamically adjust the congestion window to improve TCP performance by reducing the congestion window overshooting problem. We study the network performance such as throughput, Packet delivery ratio, and end-to- end delay when congestion control mechanism is used.

Wireless data services are fundamental in ubiquitous networks. In wireless data networks, the TCP congestion mechanism can mistake a wireless channel error or blackout for congestion on the route. Several wireless TCP protocols have been proposed considering TCP performance degradation in wireless systems. However, these protocols are too complex to deploy in wireless systems. In this paper, we propose the ACK Pacing algorithm for long lasting loss periods like a hand-off or a blackout. By pacing ACK packets sending, we prevent bursty data delivery to the old path and a spurious timeout occurrence. Also, paced ACK packets trigger the route update to the new path faster. The proposed algorithm can be implemented in the wireless-node-side which is easily applicable to wireless systems. From simulation results, ACK Pacing improves TCP performance compared with many TCP variations. The ACK Pacing algorithm shows good performance during a long lasting loss period.KeywordsMobile NodePacket LossCorrespondent NodeCongestion Window SizeWireless LossThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

There have been some rapid advances on the design of full duplex (FD) transceivers in recent years. Although the benefits of FD have been studied for single-hop wireless communications, its potential on throughput performance in a multi-hop wireless network remains unclear. As for multi-hop networks, a fundamental problem is to compute the achievable end-to-end throughput for one or multiple communication sessions. The goal of this paper is to offer some fundamental understanding on end-to-end throughput performance limits of FD in a multi-hop wireless network. We show that through a rigorous mathematical formulation, we can cast the multi-hop throughput performance problem into a formal optimization problem. Through numerical results, we show that in many cases, the end-to-end session throughput in a FD network can exceed 2x of that in a half duplex (HD) network. Our finding can be explained by the much larger design space for scheduling that is offered by removing HD constraints in throughput maximization problem. The results in this paper offer some new understandings on the potential benefits of FD for end-to-end session throughput in a multi-hop wireless network.

The effective provision of real-time, packet-based voice conversations over multi-hop wireless networks faces several stringent constraints not found in conventional packet-based networks. The wireless links in an ad hoc network are highly error prone and may go down frequently because of node mobility, interference, channel fading, and the lack of infrastructure, it is very difficult and challenging to implement voice transmission over multi-hop wireless networks. In this research, to maximize the performance of multi-hop wireless networks during voice transmission we choose some parameters and methodological approaches e.g. Since voice applications consume more energy than typical applications, we designed the ad hoc and adaptive control model to simulate our scheme.